How Can I Achieve Function Pointer Functionality in Java?

What to Use Instead of Function Pointers in Java

In the Java programming language, function pointers, a feature that allows one to pass functions as arguments to other functions, are absent. However, there are alternatives to achieve a similar functionality.

One viable option is anonymous inner classes. Consider the need to create multiple methods that perform the same operation except for a small variation in a single line of code. Anonymous inner classes offer a solution.

To utilize anonymous inner classes, an interface must be defined, declaring the method that will be passed in. For instance, if the method takes a String parameter and returns an integer, the interface would resemble this:

interface StringFunction {
    int func(String param);
}

A method that accepts the function pointer would accept an instance of the StringFunction interface, as shown:

public void takingMethod(StringFunction sf) {
   int i = sf.func("my string");
   // do whatever ...
}

To invoke this method, use anonymous inner classes like so:

ref.takingMethod(new StringFunction() {
    public int func(String param) {
        // body
    }
});

In Java 8 and later, lambda expressions provide a more succinct alternative:

ref.takingMethod(param -> bodyExpression);

This allows for passing a function as an argument in a concise and readable manner, effectively emulating the behavior of function pointers.

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